Modern dishwashers typically incorporate a spray arm located in the lower region of the interior space of the dishwasher cabinet, which arm is rotated as by water jet reaction forces while rotating a plurality of washing jet sprays directed at the dishware items by directing a washing liquid under pressure through nozzle openings formed along the length of the spray arm. In order to wash both the front and back of items such as plates, which typically are racked so as to lean back, forwardly and reversely angled jet sprays have been utilized in addition to vertical jets, but this requires additional pump flow in order to achieve total coverage of the dishware items.
Also, in using fixed angle jet sprays, a certain amount of shadowing of the jet spray may occur at each rotational position of the spray arm. That is, portions of the jet sprays may be intercepted by dishware surfaces before impingement on dishware surfaces positioned remotely therefrom, as viewed along the direction of the jet spray.
It has heretofore been proposed to oscillate or rotate the spray arm about its longitudinal axis as the spray arm rotates about a central transverse axis to thereby vary the angle of the jet sprays as the dishwasher spray arm rotates.
The oscillation has been described as being carried out by means of a jet reaction wheel, positioned within a housing which receives water under pressure from the circulation pump and directed in a jet at the reaction wheel to cause the reaction wheel to rotate. The rotation of the reaction wheel in turn produces oscillation of the dishwasher spray arm about its longitudinal axis by a gear driven crank mechanism. The forces producing rotation of the spray arm about its central transverse axis are produced by a difference in reactions of jet sprays on either side of the spray arm on opposite sides of the rotational axis. Accordingly, as the spray arm oscillates in one direction, the asymmetrical arrangement of the reaction jets on one side could cause changes in the differential forces acting on the spray arm during oscillation such that the torque acting on the spray arm may vary as the oscillation of the spray arm takes place. The result is a variation in rotational speed of the spray arm which cannot therefore rotate at a single optimal rate at which the best washing action is achieved.
In addition, this requires two different sets of jets for washing the front and rear of dishes to thus increase the flow requirements of the pump supplying the washing jets.
Also, the use of a submerged reaction wheel and gearing around which is circulated wash water bearing solids washed from the dishes may lead to less than reliable operation since jamming of the gears from accumulated solids would be likely.
In another arrangement which has been proposed, the spray arm is described as being caused to rotate by means of a fixed reaction gear cooperating with a gear carried on the spray arm, which is mounted for rotation about its longitudinal axis as well as about its central transverse axis. As the spray arm rotates, the fixed reaction gear causes rotation of the spray arm about its longitudinal axis. In this arrangement, the spray arm is required to have diametrically opposite jet pairs which serve to balance the torque in all positions of the rotary spray arm about its longitudinal axis, such that the rotation thereof does not produce a variation in torque. However, this necessitates that one end of the spray arm cannot be rotated since one end of the spray arm is required to produce the jet reaction forces necessary in order to impart rotation of the spray arm as a whole. In addition, a 360.degree. rotation of the spray arm obviously is not suited to bottom-mounted spray arms as the jet sprays must be directed generally upwardly in order to contact the dishware.
It can be appreciated that the above-mentioned desirability of a varied attitude of the washing jet sprays to produce maximum coverage of a single set of jet nozzles, and to prevent shadowing applies to each rotational position of the spray arm. That is, a variation in jet angle at every rotational position will increase the coverage and reduce the degree of shadowing which will occur with the spray arm in that position. Neither of the above-mentioned proposals describe an arrangement for accomplishing this result.
In addition, any such design feature should desirably not introduce undue complexity to the dishwasher and should operate reliably since the manufacturing costs and consumer acceptance of such products are of considerable importance in their design.
Accordingly, it is an object of the present invention to provide an arrangement for producing oscillation of the rotary spray arm about its longitudinal axis so as to cause a varying washing jet spray attitude with respect to the dishware as the spray arm rotates such that each jet spray is directed in a forward, reverse and vertical inclination with respect to the dishware.
It is still another object of the present invention to provide such an arrangement in which the oscillation does not result in a variation in jet reaction forces on the spray arm tending to produce varying rates of rotation thereof, and which allows the entire length of the spray arm to be oscillated.
It is a further object of the present invention to provide such an arrangement in which a number of jet spray angles with respect to the dishware items are achieved in each rotational position of the spray arm.
It is another object of the present invention to provide such features with a simple and reliable design of the spray arm and mounting structure.